The present invention relates to a diaphragm module for pneumatic control systems and particularly to such a system having a pressure comparing stage for converting an applied pressure difference into a force and a force/pressure transducer being controlled by the pressure comparing stage wherein, in a multiple-part housing, chambers are formed by comparing and tightening diaphragms with pressures to be compared with each other being applied to said chambers and wherein by means of diaphragm disks loosely piled up in the housing and being admitted by the comparing diaphragms the resulting force is accordingly converted into a displacement of the diaphragm disks. This diaphragm module may be used for the control of process variables in such devices as fluid-operated controllers, ratio relays, summation relays, etc. In known devices of this kind, as for instance described in the book of Hengstenberg "MeBen und Regeln in der chemischen Technik", Springer Verlag 1964, pages 1159 and 1179, in particular under reference to the diagrams 127 and 136, the whole diaphragm package is rigidly interconnected by means of a leading-in pin. Rigid clamping of the diaphragm disks to the diaphragms as well as leading through and fixation of said leading-in pin complicates centering of the whole diaphragm package and its parallel alignment with respect to the nozzle of the pressure/force transducer in those known controllers. In order to prevent an undesired hysteresis, a break in the characteristic and changes of the diaphragm areas, respectively, the known controllers use double diaphragms with an enforcement and with a vented interspace. Not only the number of required diaphragms is doubled, but the whole design becomes complicated which is an obstacle to the miniaturization of the device.
A pneumatic diaphragm module known from German Pat. No. 25 29 457 achieves an improvement with this respect. With this module the diaphragm disks are loosely stacked in the housing, wherein flat and thin comparing diaphragms are arranged between the disks and act to displace said disks. Tightening diaphragms having a negligible active area separate the individual stages from each other. Centering of the whole package of diaphragm disks is achieved by matching the diameter of the diaphragm disks to the recess of the housing. In order to provide an active diaphragm area, it is necessary to step off the diameter of the diaphragm disks. Whereas this known diaphragm module has given satisfactory results, problems with respect to permissible limits and friction arise due to the matching of the diameter of the diaphragm disks to the recess of the housing. This is particularly true if molded plastic parts are used.